Electromagnetic
energy is the compression and rarefaction of waves of magnetic fields
and electric
currents traveling through the vacuum of space or the
atmospheres of planets. The sun is a source of electromagnetic
energy. It generates magnetic fields that discharge electric
currents which produce magnetic fields that again discharge electric
currents. This is the cycle of electromagnetic energy.
The
electromagnetic spectrum includes gamma rays, x-rays,
ultraviolet light, visible light, infrared heat, microwaves, and
radio. Visible light and radio occupy a small fraction of the
electromagnetic spectrum.
The
electromagnetic spectrum, as sound
and ocean waves, can also be described
in terms of frequency,
wavelength, amplitude, and if applicable subjective intensity.

Handbook
Note:
Nano = one billionth or 1/1,000,000,000
A
nanometer or nm = a billionth of a meter
A
trillion = 1,000,000,000,000

Visible
Light
Visible
light is the compression and rarefaction of visible
electromagnetic waves.
An initiating disturbance
such as
the sun or an artificial light source starts the cycle of visible
electromagnetic energy. The cycle continues until it
terminates in
our eyes or fades away. White
light shone through a prism separates into a rainbow of all the colors of
visible light. The wavelengths
of visible light range from 400 nm
to 770 nm. The
wavelength of the color red is 570 nm, green 540 nm,
and blue 440 nm. Invisible light with wavelengths shorter than 400 nm is the
ultraviolet spectrum. Invisible light with wavelengths longer
than
770 nm is the infrared spectrum. The
frequencyof
visible light is measured
in the trillion of cycles per second. This is a
range of 400
to 750 trillions ofcycles
per
second.
Note that this
is a very narrow range when compared to theten-octave
range of the ear. The amplitudeof
visible light is defined as its intensity. The intensity of light
is measured by its directional radiating power or luminance. Luminace is measured in units of lumen,
which ranges from 0 to more than 12,000 lumen. As a reference,
consider
the following: -
Indoor
artificial light ranges in amplitude from 400 to 600 lumen.
-
Outdoor
brightness ranges from 1000 to 12,000
lumen.
-
Your
eyes are comfortable to a level of about 3,500 lumen.
- 4,000
lumen becomes glare.
- At 10,000
lumen our eyes block light.
-
12,000
lumen is the amplitude of snow blindness. The percieved subjective intensity of light by the human eye is defined as brightness. Brightness is to light as loudness is to sound. And similar
to the loudness response of the ear -- the eye is not equally sensitive
to the entire bandwidth of light. The eye is most sensitive to the
wavelength of greenlight, less sensitive to the wavelength of
red,
and even less to blue
light.Furthermore,
the amplitude of light creates two states of vision - scotopicand photopic. The scotopic
state is our adapted nightvision.
It involves the
rods of the eye’s retina, which are very sensitive to the intensity
of light. But their sensitivity is limited to the shorter blue
colored wavelengths. The photopic
daylightstate involves the cones of the eye’s
retina, which are sensitive
to the entire spectrum of color. But they are much less
sensitive to
the intensity of light.

Radio
is the compression and rarefaction of invisible
electromagnetic
waves of energy. An initiating disturbance such as the sun or a
radio broadcast antenna initiates this cycle that
terminates at a receiving antenna or fades away.For
example, a radio broadcast begins with modulating electric current in a
copper wire, the broadcast antenna. This generates
cycles
of
electromagnetic waves. The electromagnetic waves cause
electrons
in a
receiving antenna to budge, dislodge, and regenerate cycles of
electromagnetic current. That is the invisible sequence of
radio.
Broadcast
radio covers a frequency
range of thousands of cycles per second as AM radio, to billions of
cycles per second as satellite TV.
The
typical car radio displays the
broadcast frequency on its front panel -- AM in KHz and FM in MHz.
The
wavelengthof
radio
ranges from a few hundred yards as AM radio to
a fraction of an inch as
satellite TV.
The
power oramplitudeofradio’s
electromagnetic
energyis
measured in watts. A watt is equal to the flow of the electrical
current in amps multiplied by its pressure in volts. The issue of a
subjective response to radio does not apply as it did with sound and
light because humans cannot see or hear
electromagnetic radio waves.Don’t
change that channel. We will return to the exciting
conclusion of
Radio in Chapter 3 following these messages. Please
stay
tuned.